


Undyne's 'fishy' sister

by LilMissLily



Category: Undertale (Video Game)
Genre: Angst, Eventual Smut, F/F, F/M, Female Reader, Fluff and Angst, I can't pun, I'm Bad At Tagging, M/M, Magic, Monster!reader, Monsters, Other Additional Tags to Be Added, Papyrus Being Papyrus, Protective Sans, Reader Is Not Frisk, Reader-Insert, Slow Burn, Slow Romance, Violence, monster reader, reader is clueless and shit, undyne being an overprotective mother fish, ur actually kinda cute and i wanna protect u from everything, you're a fish
Language: English
Status: In-Progress
Published: 2017-10-09
Updated: 2017-11-11
Packaged: 2019-01-15 05:38:26
Rating: Not Rated
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 3
Words: 5,088
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/12314823
Author URL: https://archiveofourown.org/users/LilMissLily/pseuds/LilMissLily
Summary: [A fanfic in which the Reader is in fact, a monster. That's right! A monster.] You're the one and only blood sister of Undyne and you know your way around the Underground. You know how intimate SOUL sharing is, the ins and outs of magic and of course the importance of getting to the surface. While monsters can get up to 200 years old, some even older, you're actually relatively young. Not a baby of course, although sometimes you're a little slow to catch up on things, you're a little too naive sometimes, an open book,- okay, well, maybe Reader is a little on the innocent/pure side, but we'll work on that as we work our way up to the Surface. One step at a time.[Yep. A very slow burn. You're gonna meet Sans and Papyrus. Meet a human. See your sister have her first date. Smooch a skeleTON. (ahaha I'm so proud of that pun) Make it to the surface. Maybe even live up there in peace? Go to different universes? You MIGHT just meet another you from another universe!]!! I don't have an updating schedule, I'll update when I have the time so you might have to wait 2 weeks or 2 hours for a chapter to be finished !!





	1. Chapter 1

**Author's Note:**

> Welp. I tried. I've seen so many reader stories but not a single one of them with the Reader actually being a monster. I'm sure there are some out there, but there certainly aren't many. Also, my English might suck? It's not my native language. I also can't pun. So yeah. Have fun reading this!

‘’BE CAREFUL OUT THERE SQUIRT!’’

‘’I will Undyne. You take care too. Tell Alphys I said hi!’’

Undyne gives you an affectionate smile, nods and leaves to Hotland.

Hotland… you unconsciously run your hand over your scale covered arms while standing in the doorframe.

You hope Undyne’s ok, you knew you two couldn’t stand the heat in there.

Not that it would get in Undyne’s way. Your sister was strong. Determined.

You should go to Snowdin, to Greater dog. You doubted that there would be a human this time, but it didn’t hurt to double check.

You turn back into the house and come back out with an elegant coat with long sleeves that went past your hands. Queen Toriel gifted you this when you and Undyne lived closer to the castle. A present for your and Undyne’s hard work. (Even though you insisted that weren’t the one that was part of the Royal guard, both queen Toriel and Undyne smiled at you pushing the handmade coat into your hands) It was warm and made up of a material that somehow kept your scales hydrated. You smiled recalling the good memories. You stepped out of the doorframe, the teeth of the fish house clamping shut.

_**____________________________________________________________** _

You wondered why you haven’t seen the queen that often anymore. You asked Undyne about it and she just gave you a tilted smile and said that she was busy doing ‘queen stuff’. You didn’t question it. Queen stuff did sound important…

*bark bark*

Surprised you looked up to see Greater dog. You almost bumped into him. Whoops.

Leaning over to the right, balancing on one foot, you look at the sentry station behind him to see if there was, possibly maybe, a human.

Surprise. There wasn’t

Your ear fins twitched as you heard Greater dog whine. Looking at you, unsure of what to do.

_Oh no, was he scared you were mad at him?_

‘’It’s okay. No worries. I know we’re close. But we just have to stay patient. It’s not like humans fall down here every day!’’ You quickly reassured him and reached out to pet him behind the ears while standing on your tippy toes. Greater dog barked in excitement and happily crouched down to your level.

You moved to sit down in the snow while Greater dog laid his head in your lap. Petting him you looked around Snowdin. Everyone looked neutral, happy, content. You looked back down at Greater dog and focused on giving him the best possible petting session. You grinned when you saw his tail wag a little faster. You could stay here until Undyne came back. No danger, no fuss, as long as Greater dog was here, you were safe.

 Your ear fins twitched as you heard a rather loud voice yell and Greater dog shot up so quick he almost bumped his head to your chin. A surge of panic went through you. What if there was a fight?! What if it was a human?!  Your breath hitched. What if people got hurt? You you've never seen one, but you’ve heard stories about how humans sealed the monsters in the Underground during the war and they didn’t exactly do it very gently.

Then suddenly, Greater dog ran off.

_NO! Nononono! Come back!_

You couldn’t do this alone! You couldn’t be alone! GOD WHERE WAS UNDYNE?!

Without thinking, you went off to run after Greater dog.

_**____________________________________________________________** _

You weren’t fast. You never were. So of course you wouldn’t keep up with G.D.

Thankfully, you saw his tail turn a corner.

‘’SANS LOOK! IT LOOKS LIKE I HAVE ALREADY MADE A GREAT FRIEND. ALTHOUGH, HE DOESN’T SEEM TO HAVE THE INTENT OF SLOWING DOWN.’’

‘’um pap, you might wanna move-‘’

‘’NONSENSE! THIS CREATURE OBVIOUSLY WANTS A HUG! I ACCEPT YOUR CHALLENGE!’’

Huffing you grabbed the corner and peeked over.

_Two skeletons?_

‘’NYEHEH-?!’’ The taller skeleton’s confident expression quickly turned into confusion and slight fear as he saw G.D  approaching and tackling him to the ground.

The shorter skeleton’s eye sockets darkened for a moment before one of his eyes flashed blue and he lifted G.D off of the longer skeleton.

_Woah…_

You gaped in amazement. You’ve never seen anyone use magic like that! You’ve seen Undyne summon spears, seen Grillby's, Asgore’s and Toriel’s fire magic, but never this!

The shorter skeleton, now with both of his hands in his hoody, narrowed his eyes at the dog as it started growling at him.

‘’SANS WAIT! BE CARE-‘’

G.D yelped.

That got you out of your daze.

‘’W-wait! Don’t hurt him!’’

Wow, you didn’t sound convincing at all.

The shorter skeleton snapped his head at you making you flinch.

That blue eye was scary…

‘’SANS.’’ The taller skeleton warned and dusted himself off.

‘’this your dog?’’ He asked while lowering G.D to the ground.

His tone made you flinch again. Which made the shorter skeleton’s gaze soften a little. Not much. Just a little.

‘’No, he’s, um, a sentry. H-he looks after the citizens here…’’ You yelped. ‘’We, um, heard someone yelling?’’

Something clicked in the skeleton.

‘’right. so he was just looking after people.’’ He muttered.

‘’i think you should work on your hearing, buddy, you shouldn’t attack the person that was yelling.’’ He glared down at G.D

You blinked before making your way to the taller skeleton.

‘’Are you okay? Do you need me to heal you?’’

The taller skeleton blinked. Then suddenly smiled.

‘’THAT IS VERY CONSIDERATE OF YOU! BUT I AM FINE! THE GREAT PAPYRUS WAS JUST SURPRISED TO RECEIVE SUCH AN…ENTHEUSIASTIC HUG!’’

G.D whined and bumped his head to yours.

‘’I know. It’s okay. Mistakes happen.’’ You reassured him and giving him a small smile.

You quickly turned to the shorter skeleton.

‘’I am very sorry for what we have caused here. We didn’t have the intent to.’’ You looked up unsure at him.

You were small. Very, very small. The shorter skeleton was just a tiny bit taller than you.

He didn’t reply though. He just kept staring at you.

‘’SANS YOU ARE BEING VERY RUDE!’’

Sans jolted a little and a small blue hue appeared on his cheekbones.

‘’s’ok bud.’’

‘’So I’ve never seen you two here before…’’ You started lamely.

The shorter skeleton visibly relaxed and put on a lazy smile. The taller one spoke up.

‘’WE HAVE MOVED HERE! AS YOU CAN SEE, THIS IS OUR NEW HOUSE! I PERSONALLY PICKED IT OUT MYSELF!’’  He proudly gestured to the house that you somehow didn’t notice standing there right next to you.

‘’yeah. it’s pretty _cool_ here.’’

The taller skeleton groaned while the shorter one curiously looked at you waiting for your reaction.

You didn’t get it.

You knew there was something that was supposed to be funny, or perhaps irritable? But you didn’t get it. You looked at the shorter skeleton with a frustrated look while one of your ear fins twitched in confusement. The shorter skeleton’s white pinpricks glanced over to your ear fins before going back to your face, that blue tint was back again and his grin had somewhat intensified?

‘’If you want, I can show you two around? I can imagine that you two aren’t familiar with Snowdin yet.’’ You fumbled with your long sleeves and looked anywhere but their faces.

What? It wasn’t wrong to make new friends!

‘’heh. that’s a very nice thing of you to do.’’

Ok. You were blushing now.

Unbeknownst to you, the skeleton’s white pinpricks glowed with amusement.

‘’THAT IS INDEED VERY NICE OF YOU! WE ACCEPT YOUR OFFER! RIGHT SANS?’’ The taller skeleton grinned excitedly before his face twisted into a look of horror.

‘’OH NO! HOW RUDE OF US! WE HAVEN’T EVEN INTRODUCED OURSELVES!’’ He straightened himself, cleared his…throat? and struck a pose

‘’I AM THE GREAT PAPYRUS! AND THIS IS MY BROTHER SANS!’’

‘’great job, bro.’’ Sans said, but not ever without looking away from you.

You wondered why…

 

 

 

Oh. duh.

 

 

 

‘’My name is-‘’

‘’NGAAAAAAAAH! GET AWAY FROM (Y/N)!’’


	2. Chapter 2

**Summary for the Chapter:**

> Sans gets to know something...interesting about Reader

**Notes for the Chapter:**

> Oh my lord, thank you guys so much for your nice comments! I didn’t expect that many people to actually like it O.o. I'm so sorry about the wait! School's getting to me T.T   
> Feedback helps a lot! Tysm! <3 (Also please point out any grammar mistakes I made, I might ask someone to double check/correct my work before I post it.)

‘’NGAAAAAAAAH GET AWAY FROM (Y/N)!’’

Sans immediately tensed and Papyrus looked like he was about to explode from excitement. You, on the other hand, noticed nothing wrong and happily waved your sister over.

‘’Undyne! How was Al-‘’

‘’YOU GET AWAY FROM HER RIGHT NOW, PUNK!’’ Undyne protectively planted herself in between you and Sans. Sans narrowed his eyes while leaning back and tilted his head up. A lazy gesture that stood for: ‘ _You’re not intimidating anyone’_ and it didn’t go past Undyne. She sneered and took a menacing step forward. Before she could even manifest her magic into a spear, she heard your voice and felt your soft hand gently grab hers.

‘’These are Sans and Papyrus! They just moved here!’’

Undyne’s face softened and she relaxed a little.

You looked like you were about to grin your face off. DAMN YOU!

‘’You punks new here, huh?’’ she cautiously got into a less aggressive stance before moving over. Not away from you. No, of course not. She went to stand next to you, holding your hand and squeezing it as if she was apologizing for her rude behaviour. You didn’t really notice though, you were busy checking on G.D.

After you finished, G.D got up and wandered back to his station.

Sans raised an amused eyebrow while Papyrus took it upon him to explain.

‘’YES! WE WERE ABOUT TO GET A TOUR BY…ERRM?’’ He glanced at you.

‘’(Y/n)’’ You nodded happily.

‘’YES. (Y/N).’’ Papyrus looked at Undyne. ’’WOULD YOU LIKE TO JOIN? THAT WAY, WE CAN ALL BE FRIENDS!’’

Undyne almost snorted at how goofy he sounded. But something told her that he was actually being serious and that it was a genuine request. Not only that, his volume, energy and overall devotion and determination to making friends almost seemed…heroic? Brave? She couldn’t describe it, but she felt slightly…interested? intrigued? curious?

 

She also didn’t want you to be alone with that shorter skeleton named Sans. His permanent grin didn’t really appeal to her, and neither did his choice of clothing. Who the heck wears slippers in this kind of weather?!

‘’OF COURSE I’LL JOIN! I NEVER REFUSE A CHALLENGE! EVEN IF IT’S MAKING FRIENDS! JUST YOU WAIT, AT THE END OF THIS TOUR, WE’LL BE BESTIES!’’ Undyne wrapped her arm around Papyrus’ neck and grinned at him. Papyrus looked up at her with starry eyes and admiration and it reminded her of you when she told you stories about how she’d make sure monsters got to the surface.

She liked Papyrus. Even if he was a huge goofball.

‘’Careful Undyne! Don’t underestimate your own strength!’’ Undyne loosened her grip a little.

You’ve seen Undyne underestimate her strength around monsters plenty of times. Not that she did it on purpose, and not that she actually didn’t know of course. She knew she was strong, but she often got a little…too passionate when it came to certain things.

Not to mention all of the times she accidentally set the house on fire.

Yep. That’s why you’re the one that cooks.

 Speaking of food.

**_*Grumble*_ **

You blushed.

‘’sounds like you _cod_ use a bite’’ Sans eagerly watched you again. Sadly, you didn’t do that adorable ear twitch again, you were probably too busy being embarrassed about the growl your stomach let out.

Not that that wasn’t adorable to look at either.

Papyrus nearly screamed while Undyne just looked at him not knowing what to say.

Fish puns.

_Fucking. Fish puns._

**______________________________________________________________ **

 

Your embarrassment seemed forgotten as soon as you took Sans by the hand and led him, your sister and Papyrus to the best possible place for food.

Grillby’s.

Sans’ smug expression as you grabbed his hand went unnoticed by you, but of course, not by your sister. She gave him the universal sign for _I’m watching you!_ Before turning her attention back to Papyrus who was excitedly rattling (lol) about how he wanted to join the Royal Guard. Undyne was thinking of recruiting him, but before she did she wanted to know a little more about him.

‘’so, where we goin’?’’

You slipped your hand out of his, much to Sans’ disappointment, and intertwined both of yours in front of you.

‘’Grillby. He’s really nice, the food is good and the people there are super welcoming! I bet you’ll feel right at home.’’ You grinned at the thought and Sans couldn’t contain the genuine smile that you got out of him.

 

Truth be told, he was actually pretty nervous. Papyrus and him had been moving around. A lot. The last few places Papyrus and him lived in hadn’t been that welcoming as you had been. Not that they were rude. Monsters were rarely rude. They just…didn’t really expect Papyrus to be that energetic. He’d never blame it on his brother, but Papyrus was the type of monster that needed socializing and, well, attention. He never purposely asked for it, but without it, he’d be less energetic and less…him. Apparently, monsters found Papyrus too loud and annoying. Sans never told Papyrus this, because in his eyes, Papyrus was the coolest monster in the whole Underground.

‘’Here we are!’’ Your cheerful voice broke him out of his thoughts. Luckily, the place wasn’t that big and skin or no skin, Sans could feel that it was warm in there.

‘’One sec sis.’’ Undyne, surprisingly, lowered her voice. She wedged herself in between you and Sans and whispered.

‘’ _Think I can borrow you coat? I need it for…you know…’’_

You blinked. Then nodded. Your coat had a hoodie attached to it, you never used it because the hoodie was way too big and it ended up covering your eyes. Undyne sometimes wore a coat in big places so that she wouldn’t be recognized, normally she’d be absolutely pumped for  the attention, but now, she had to test Papyrus, without him knowing that she was captain of the Royal Guard.

‘’ _Can you wait until we’re inside? My scales are more sens-‘’_

_‘’Yeah! Yeah, of course! I’ll just hang around in a corner or something.’’_

You nodded and jumped when you saw Sans…judgingly watch Undyne?

Huh. Could he have heard the conversation you and Undyne were having?

(Yep. He was standing next to you the whole time)

‘’Um, let’s go in then?’’ You asked a little unsure as he kept following Undyne with his gaze. He looked back at you and nodded. His lazy grin returning when he laid eyes on you.

As soon as you pushed the door open, warm air greeted you as well as cheerful chatting and the delicious smell of food. Grillby looked up from the glass he was cleaning behind the bar to give you a friendly nod and curiously tilted his head to Sans and Papyrus.

You smiled in return and grabbed Sans’ hand again, gently tugging him to sit at the bar, right in front of Grillby, before hurriedly going back to Undyne and wiggling out of your warm coat. Papyrus, being the social butterfly he is, had already been busy chatting with some other monsters. You handed Undyne your coat and she quickly put it on, using the hood to cover a good portion of her face.

_‘’How do I look?’’_

You stepped back to take a look at her.

‘’ _Wait, this part isn’t entirely covered.’’_

You reached up and pulled down the hood a little more and nodded satisfied. Undyne muttered a ‘thanks’ before rustling your hair and walking towards Papyrus.

You unconsciously went through your hair with your hands and looked back at Sans sitting at the bar. To your surprise he wasn’t sitting alone. A small crowd had formed around him, laughing and listening intently as his grin widened with every pun he told.

Silently walking around the crowd and sitting on the bar stool next to Sans you watched for a few minutes as he kept telling puns. After some time, you got a little tired and frustrated of trying to figure out the punch-lines and other jokes so you tapped him on the shoulder.

Sans took note of the soft scales timidly tapping against his shoulder, quickly ended the pun and looked to his left before blushing bright blue.

Because hey, you had a tail!

But that’s not what he was flustered about.

The monsters that had grouped around Sans were grinning and giggling knowingly at Sans, knowing that his expression was once theirs when they first met you and Undyne.

 _Undyne_ wore clothes and because you were her sister, they expected you to wear them too. But no, underneath that thick handmade coat, was a smooth, soft light blue layer of scaly skin.

**Notes for the Chapter:**

> Don’t worry! Reader doesn’t actually wander around the Underground naked! Think of it as fur! Or a second skin! You know Ruto, princess of the Zora from the Legend of Zelda? I based Monster!Reader on her! (Look up some pictures, I absolutely love her character design in Hyrule Warriors) And, about Reader having genitalia and how it works...that’ll be a story for another time. It’s… a sansistive subject ;)


	3. Chapter 3

**Summary for the Chapter:**

> Snas pls. calm down. snas. i meant it. pls

**Notes for the Chapter:**

> WHOOO OKAY. SORRY FOR THE WAIT. HERE IT IS. HAVE FUN! I also want to thank so many of you who have been thinking about names, support the story and have complemented her design! I luv u guys >///^\\\\\<. I’ll have to think about an actual name/nickname but I’ll let you guys know. I might not always reply to most of the comments but I do read them all and so many of you are such nice marshmallows and I just want to hug and cuddle you guys! k im being creepy. enjoy!

You giggled silently. You had seen that expression of surprise so many times when you took off your coat. You weren’t completely innocent, you knew why. (you actually didn’t know at first, Undyne had to explain it to you)

‘’Sans? Are you okay?’’ You chuckled. His face looked so confused!

‘’uh…you….you got a tail?’’ Sans watched you grinning at him and nervously darted his eyes back to your swishing tail behind you.

‘’Oh! Yeah! It’s surprising isn’t it? Seeing how Undyne doesn’t have one.’’ You curled your tail so that it was now lying in your lap.

It had soft fins decorating the sides that were a darker shade of blue and at the tip of your tail was a mermaid-like-shell-shaped-fin.

‘’can i-?‘’ Sans reached out to touch your tail and you quickly moved it away blushing brightly.

‘’Uhm, no, I mean…yes? But I…um…you see-it’s um…VERY sensitive and um, you know….’’

‘’oh. right. sorry.’’ Sans pulled his arm back grinning apologetically. You murmured an ‘’It’s okay’’  your face still a little hot from embarrassment and quickly changed the subject.

‘’So, have you thought of what job you want to get?’’

  ---------

‘’So, Papyrus, I wanted to ask you some questions.’’ Undyne started as she pulled Papyrus away from the table.

‘’OF COURSE! THE GREAT PAPYRUS IS ALWAYS READY FOR QUESTIONS!’’

Undyne smiled at his enthusiasm.

‘’Could you tell me what think of humans?’’

Papyrus gave Undyne a thoughtful expression.

‘’HUMANS? I’VE…NEVER SEEN ONE BEFORE.’’

‘’It doesn’t matter what they look like, how old they are, how they… _act,_ I just need your opinion on them.’’

‘’ERR…I SUPPOSE THAT I AM UNCERTAIN? I KNOW THAT THERE WERE SOME HUMANS THAT DISAGREED WITH US AND PUT US HERE THOUGH.’’

‘ _disagreed?’_

Undyne’s face scrunched up.

‘’Ok. Fair enough.  What are your STATS?’’

‘’MY STATS?’’

‘’Y’know, your attacks? Your magic?’’

‘’ERM. I DON’T…KNOW?’’

‘’I guess we’ll stop by our house later then…’’ Undyne muttered.

‘’NYEH?’’

‘’Nothing.’’

 ---------

‘’i’m not really sure about that actually. paps and i just moved here, looking for a job was something we were going to do when we got familiar with the place.’’ You nodded. ‘’you suggesting anything?’’ Sans looked at you with a raised eyebrow. ‘’Well…we’re low on sentries here in Snowdin and seeing how Snowdin is the first town you enter after leaving the ruins, I think it’s something we really need to fix soon.’’

Sans’ eye sockets went black.

‘’sentry duty for humans you mean?’’

‘’Y-yeah…’’

‘’i don’t think i’m fit for that kind of job. sorry bud.’’

You shook your head.

‘’It’s fine. It’s not like there are a lot of humans that fall down anyway. I’m sure we’ll figure something out in time.’’

 

‘’READY TO GO (Y/N)?’’

Your ear fins twitched at the sudden loud noise.

‘’Already?’’

‘’YEP! WE’RE GOING TO OUR HOUSE AND PAPYRUS IS GONNA JOIN.’’

_Oh you knew what that meant._

‘’Sans, you might want to come with us.’’ You turned to Sans to see him looking at Papyrus.

‘’wherever paps goes, i’m right onto his tailbone’’

‘’THAT’S HIGHLY INAPPROPRIATE SANS!’’

‘’heh.’’

 

‘’Sans?’’ Undyne whispered.

‘’what’s up fishface?’’ Sans replied a little irritated to how close Undyne was to his skull.

‘’DON’T USE THAT NAME ON ME!’’ Undyne flared before letting out a huff and asking;

‘’What are Papyrus’ STATS?’’

Sans stopped walking.

‘’why do you wanna know?’’ Sans narrowed his eyes suspiciously. STATS were actually a very private thing. It lets someone know exactly how many hits you could take and how much damage one could do.

‘’I’m thinking about recruiting Papyrus into the Royal Guard.’’ Undyne replied casually.

‘’ d o n t ‘’

‘’Excuse me?’’ Undyne turned.

‘’paps isn’t that kind of monster. he can’t.’’

‘’I’ve heard him talk on and on about how he wants to join the royal guard and don’t you think I sensed how strong his magic is? I’m leader of the royal guard for a reason Sans.’’

‘’papyrus can’t kill, he’s not that kind of person.’’ Sans forced and glared.

‘’I’ll find out for myself, I don’t need you to be the judge of me.’’ Undyne walked away from him unknown to her that Sans’ eye had started glowing a dangerous blue.

 

* * *

 

‘’Okay Papyrus. Let’s just cut to the chase. I’m Undyne. THE Captain of the Royal Guard, and I have decided to test you to see if you are worthy to join.’’ You dreamily watched Undyne while sitting next to a very tense Sans.

Papyrus looked like he was going to faint and Undyne looked at him proudly.

‘’NOW STAND AND FIGHT ME. SHOW ME YOUR STRENGTH AND BRAVERY!’’

Papyrus quickly stood up and you finally took note of how tense Sans was.

‘’Sans? Are you-?’’

_WOW. OKAY. The air around him shifted and it was almost as if you could feel his magic on your face like the warmth of an oven. He’s on edge. He’s not showing it, but he’s having trouble keeping his magic contained._

*flicker* *flicker*

 

**UNDYNE  [HP 1500|AT 50|DF 20]**

**PAPYRUS [HP 680|AT 20|DF 20]**

 

_Not bad…_

Undyne grinned.

Not exactly the best, but training him would definitely be worth it. She could see him being one of her stronger trainees.

 

She’ll go easy on him. If things got too rough or she gets a little too excited, you were there.

 

‘’Alright Papyrus, show me what those tiny bones can do.’’

 

’’WHAT SHOULD I DO FIRST?’’

 

 ‘’Hm. Show me how you’d attack a human when you first see them.’’

 

Papyrus looked thoughtful for a second. Before nodding to himself

 

‘’ALRIGHTY THEN. I’M GOING TO ATTACK NOW.’’

 

Undyne rolled her eyes.

 

_You’re not supposed to tell your enemy that, goof._

 

Undyne eagerly bent her knees and got into a position that allowed her to dodge easily.

 

***Papyrus  is preparing an attack.**

 

_Seeing as he’s a skeleton, he’ll probably either throw bones at me through the air or make them rise up from the ground.  Then again, never underestimate your enemy._

 

Undyne got ready to jump as she felt a small tremble in the ground, signaling that her last guess was right.

She focused on Papyrus’ hands for any movement. Most monsters used their arms to incline in which direction they were gonna send their attack.

 

As predicted. Papyrus raised his arm, ready to summon his attack and let out a…war cry?

 

‘’NYEH!’’

 

Undyne got ready to jump and-

…

_What._

A bone was making their way to Undyne.

A small bone.

A small, slow bone.

It wasn’t even being launched! It was literally taking it’s precious time getting to Undyne.

Um.

Should she feel insulted?

Noticing Undyne’s puzzled face, Papyrus quickly went to help.

‘’I SEE YOU’RE HAVING TROUBLE TRYING TO FIGURE OUT WHAT TO DO. YOU SHOULD-‘’

A vain popped out of Undyne’s head.

‘’Papyrus.’’

‘’YES?‘’

‘’Papyrus is this a joke? We both know that bone isn’t gonna hit anything.’’ Undyne yelled a little too harshly and saw Papyrus flinch. She couldn’t help but feel insulted at that small thing still making it’s way to Undyne

‘’WELL, YOU SEE, ON THE WAY HERE, YOU MENTIONED THAT HUMANS WERE ‘PUNY’, ‘WEAK’ AND ‘COWARDLY’. SO, I THINK IT IS FAIR THAT I SHOULD GIVE THEM A CHANCE TO SHOW THAT THEY DO IN FACT, HAVE A CHANCE-‘’

‘’Papyrus. You DO know how strong a human soul can be right?’’

‘’ERR…YOU TOLD ME-’’

‘’PLEASE don’t tell me you just blindly believe what everyone says to you.’’

‘’WELL, THEY SAY THINGS FOR A REASON AND-‘’

‘’Do you even know what ‘capturing a human’ means?’’

‘’OBVIOUSLY IT’S BEFRIENDING THEM! OR…IF THAT DOESN’T WORK, MAYBE CHARM THEM? IT’S A CRUEL THING TO DO, TO PRETEND TO HAVE FEELINGS FOR ONE OTHER, BUT I AM SURE THAT WE CAN TALK IT OUT EVENTUALLY.’’

Undyne just gaped at Papyrus.

He looked at her with an innocent smile.

‘’Papyrus, you…’’

_Y o u  I d i o t!_

‘’It…it doesn’t work that way…’’

_D o w n  h e r e  ,  i t  ’s   k i l l  o r  b e  k i l l e d!_

She clenched her fists

Undyne, as powerful and brave as she was,  didn’t have the strength to tell him that he would have to kill someone. She recognizes his ‘stubborn-ness’. She has it herself too. But she calls this Determination.  He’s…determined too. But with different goals.

She couldn’t let him into the royal guard. He was going to get himself killed. But the way he spoke to her… He was so passionate about joining the royal guard. So full of himself, so…optimistic. She knew he had a kind SOUL when he told her about how many friends he was going to get by joining. And her SOUL hurt a little when she heard about how ‘shy’ monsters were with befriending him. He not only admired her, joining the royal guard was his DREAM! And she…couldn’t break something like that.

‘’Papyrus, you-‘’

‘’You’re absolutely right!’’

Undyne stared at you in confusion as you made your way to Papyrus.

* * *

 

‘’Sans, it’s okay! Undyne wouldn’t hurt Papyrus! She knows that this is just a test, not a real fight.’’

Sans just growled.

You flinched.

‘’If…if something _does_ go wrong,’’

Another wave of anxiety and rage contained magic hit your senses.

‘’Which absolutely doesn’t happen.’’ You quickly added.

‘’I can heal them, both. I don’t want to brag, but being the little sister of an overprotective sibling often results to the older sibling being a little too protective and hurting someone they didn’t really mean to hurt. I’ve seen Undyne at her worst (and trust me, you DO NOT want to mess with Reader when Undyne’s around) and I’ve healed people that were less than three breaths away from their HoPe completely draining.’’

Something about your voice…it…wavered a little. And something told him that ‘less than three breaths away from losing their HoPe’ wasn’t just a random sentence you had made up to calm Sans down.

Not to mention that _your_ _magic_ was playing a slow and steady tune to calm ~~him~~ his magic down.

He, for one of the few times in his monster life, let his guard down allowed you to work your magic around his SOUL and surrendered to your song.

*** _thanks kid._**

**_*Anytime Sans._ **

You watched it all, holding your breath. Ready to jump in if they took this a little too serious. Part of you wanted to see Undyne in action and was excited to maybe see some new kind of magic coming from Papyrus. Monsters each varied greatly when it came to magic and you didn’t doubt about Sans and Papyrus having some impressive tricks up their…uh….sleeves? But when you saw that bone attack? You were just as confused as Undyne.

When he explained how he would capture a human Sans shook his head with a stained grin and you couldn’t help but smile a sad smile.

_How nice it would be, if things worked that way._

You then noticed how broken Undyne looked. She obviously didn’t want to tell him how it really worked or that she couldn’t let him in the royal guard.

_(Y/N) TO THE RESCUE!_

* * *

 

 ‘’That’s exactly how it works Papyrus! In fact, we do something very special for humans in the royal guard!’’

Undyne stayed silent.

‘’YOU DO?’’ Papyrus asked curious.

‘’Mhm! We create puzzles to capture humans with!’’

‘’WOWIE! THAT’S A REALLY COOL IDEA!’’

‘’Yep. Since, you, uh, aren’t familiar with puzzles yet. I’ll share a secret with you. The quickest way to someone’s heart, is through the stomach.’’

‘’NO IT’S NOT! IT’S RIGHT THROUGH THEIR-‘’

You glared desperately at your clueless older sister. She returned your look with a ‘Lying is bad’ look before her eyes flashed with realization and her previous look got replaced with an ‘OOOOH! I SEE WHAT YOU MEAN NOW!’ look.

‘’Nevermind.’’

‘’Right, through their stomach, so, why don’t you start with cooking lessons?’’

‘’THAT SOUNDS LIKE A WONDERFUL IDEA!’’

While Papyrus enthusiastically beamed about puzzle and meal ideas with you, Sans had made his way to Undyne.

‘’told ya.’’

‘’Shut up, skeleton.’’

‘’oh, we’re gonna call each other by race now? alright then, fish.’’

‘’UGNNN, JUST TAKE YOUR NAÏVE LITTLE BROTHER HOME SANS, HE’S GOING TO BE THE DEATH OF ME.’’

They both inhaled sharply at that.

‘’ i appreciate you not breaking his dreams.’’

‘’I’ve seen (Y/n)’s face when I told her she couldn’t join a few years ago. I couldn’t bring myself to see another one.’’ It was absolutely heartbreaking to see you try to contain your tears and not cry in front of her.

‘’she too huh? heh. siblings.’’ Sans grinned another tired grin.

‘’They’re both too kind for this world.’’ Undyne smiled gently as she saw you talk with Papyrus.

‘’say…that sentry station…’’

‘’I know, it’s probably gonna be one closer, if not in Snowdin. Closer to other monsters.’’

_Safer._

‘’not what i meant. but that’s reassuring to hear. what i wanted to say: is the sentry station that’s in front of that one occupied?’’

Undyne narrowed her eyes.

‘’No…?’’

‘’i’ll take it.’’

‘’What?’’ Undyne looked surprised at Sans

‘’i’m not taking any risks. if a human falls, i’ll be the first to see it. i’ll take it directly to you. that way nobody gets hurt.’’

Undyne looked at Sans as he stared back up at her with a lazy smile.

‘’i’ll come back here when I bring paps home.’’

She grinned.

‘’It’s fine. I trust you to do your job. No testing required.’’

Sans wore a look that screamed disbelief.

‘’You wouldn’t do that to your brother. Dying on him, I mean. Number one overprotective sibling rule.’’

‘’heh.’’

**Notes for the Chapter:**

> GOD THIS TOOK FOREVER. DID YOU GUYS NOTICE THE TOTALLY SUBTLE FLOWEY LINE I FORCED IN THERE? Yeaaaaaa, he’s gonna be appearing in this series too. Also, sensitive tail. Yep. I’m gonna have so much fun with that later. And would you look at that. Sans and Undyne bonded. Sort of? Next chapter is gonna be featuring Sans meeting Toriel, Your fish house on fire and some more about Reader’s magic/souls! We’re getting close to meeting the human too! I wonder what route they’ll take…  
> [For those that might be confused: *this means that they're communicating through their souls.]


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